Circuit for controlling 3 DC motors

Question

I have a simple 3 motor robot arm. Without much experience or knowledge, I put together a circuit for controlling it. Circuit is below:

Now the circuit actually works and I can program the Arduino and have it move about as I wish. Here are the issues and questions I have:

• I have had several motor drive boards "smoke" and then never turn on again. Is this because the motors may have been stalled when I powered on the circuit? I.e. if my motors have a stall current of 20A, do I need a motor driver that can handle 20A? The reason I went with less (13A drivers) is because I was only planning on operating around 10A, which would be the max power operating point. Do I even have control of how much current is drawn?

• Is it advisable to use 1 battery like I am doing? I had to strip the other end of the aligator clips, strip the 3 sets of wires, wrap em around, and apply a lot of solder. I have no idea what the "reasonable" thing to do here is, maybe it's to have 3 batteries for all I know.

• I am using AWG wire #16, which is supposed to have a max chassis wiring limit of 22A (http://www.powerstream.com/Wire_Size.htm). Should this be alright? I haven't had any wire melting problems.

• Any other suggestions are welcome, I am new to this =)

Thanks for the help, and let me know if you need any additional information.

Answer 1

Your system looks right, this is how I would do it.

1. If you had a motor driver smoke out then the voltage was too high or the current was too high or no back EMF protection. If you plan on running the motor at 20A max then your driver should be capable of dealing with 24A, at least. Don't forget that even if your motor draws 20A when stalled there is probebly is very short 30A-35A 'spike'. Always plan on 10%-30% more when selecting components.

2. Both option would work but it would be better to use a single battery for the sole reason that your system will last longer. As long as you have large enough capacitors on your driver there shouldn't be any problem running all your motors from the same battery.

3. Again, if you plan to run your motors at 20A it would be better to use a 14AWG wire that can deal ~30A. If this is a hobby project and your wires are not many meters long please don't save 2$ on wires. If you are going to make a million units then your should go for a 18AWG wire as this might be enough if you draw 20A for a very short period of time.